Australia's cheapest petrol days

AUSTRALIAN motorists could save as much as $200 a year on fuel by boycotting the bowsers on Thursday and Fridays.

One of the most comprehensive independent studies of petrol prices ever undertaken in this country has revealed the end of the working week is the peak in 90 per cent of 114 cities and towns analysed.

There was not a single place where either Thursday or Friday was the cheapest day to fill up, yet that was when demand peaked, the study's author, University of New England economics professor Abbas Valadkhani, told News Limited. The ACCC also found that Thursday was the day of highest demand in Sydney, Melbourne, Brisbane and Adelaide in 2012.

By shifting purchases to the cheapest days "motorists can counter-attack" against petrol retailers, Professor Valadkhani said.

"Everyone in Australia, avoid Thursday and Friday that is the message," he said.

In nearly two-thirds of locations, the cheapest day to buy fuel was Tuesday. Sunday was best in one-in-five places.

Publicly funded and published in the revered journal Energy Policy, Professor Valadkhani's analysis of seven years of data identifies 16 locations where the potential savings are significant.

These have the strongest price cycles - and all are either mainland state capitals or major regional centres.

In Queensland they are Brisbane, Caboolture, Caloundra, Gold Coast, Ipswich and a region including Maryborough and Gympie. The NSW locations are Sydney, Newcastle and Wollongong. Canberra is also on the list.

Metropolitan Adelaide is the only South Australian location on the shortlist – but it had the largest potential saving of 5.4c/L by purchasing on Tuesday instead of Thursday.

Metropolitan Melbourne, Geelong and Sunbury were the only Victorian locations on the shortlist.

The more significant price differentials identified by Professor Valadkhani offer a motorist who buys on the day with the cheapest average an annual saving of as much as $200 if filling a family-sized car weekly.

"Motorists can certainly get a better deal if they are conscious of the fuel price cycle," said Australian Automobile Association executive director Andrew McKellar.

"If they do seek out information about when the price is at a peak and when it's dropping they can use that to their advantage."

Mr McKellar said the "constraint" on Professor Valadkhani's findings was that the price cycle had "changed substantially in the past 18 months". ACCC research suggested the changes began in 2010.

The cycle is now less predictable. Rather than being seven days in length, it tended to be 10-12 days long. That meant the day of the peak and trough changed.

"The fact that it's less predictable works to the advantage of the major retailers in the market," Mr McKellar said.

"The unfortunate reality for many motorists is that they get ripped off by the vagaries of the cycle."

In Brisbane, the ACCC's monitoring of petrol prices in 2012 found the peak of the cycle was most common on a Saturday and least common on a Tuesday or Wednesday. The low occurred most often on a Wednesday.

In Sydney, the high point was most commonly on a Saturday then Thursday. There was not a single peak on a Tuesday. Low points were most frequent on Wednesdays and Fridays.

In Adelaide, the top was most common on a Wednesday. However, this was also the day when the bottom was most common, along with Sunday.

In Melbourne, the peak of the cycle was most common on Sunday then Thursday and least common on a Wednesday. The low was most common on a Wednesday.

Professor Valadkhani said his research showed that motorists in rural areas "never enjoy the discount day".

And he found that the price impact of long weekends and public holidays were "insignificant" when compared to day-of-week differences. This is consistent with earlier findings by the ACCC.

The Australian Institute of Petroleum - which represents BP, Mobil, Caltex and Shell - did not respond to repeated requests for comment.

The AAA's Mr McKellar said he supported the ACCC's investigation of the way fuel retailers share information. The ACCC launched a probe last year, which is ongoing.